WSJT-X/AudioDevice.hpp
Bill Somerville 8263c52240 Fix defects in audio down-sampling on some platforms.
The filter used for 4 times down-sampling cannot handle sample streams
where the hardware or drivers deliver chunks of data that are not
multiples of 4 frames long. This seems to be prevalent on some Linux
platforms. Also de-interleaving of single channel audio from stereo
streams was no longer supported.

I have changed the input strategy to de-interleave the incoming
sample stream into an intermediate buffer large enough to hold all the
samples required for a single unit of processing (one basic waterfall
interval) and apply the down-sampling filter to the whole intermediate
buffer just prior dispatch to the FFT generator.

This now means that we are now using the ubiquitous 48kHz hardware
sample rate for both input and output of audio across all platforms
and decoding a single channel of a stereo stream is again
supported. The down-sampling to 12kHz is done with a high quality FIR
49-tap low pass filter specifically designed by Joe (K1JT) for
operation in a 4kHz bandwidth.



git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx@3585 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
2013-09-28 18:34:27 +00:00

105 lines
2.0 KiB
C++

#ifndef AUDIODEVICE_HPP__
#define AUDIODEVICE_HPP__
#include <QIODevice>
class QDataStream;
//
// abstract base class for audio devices
//
class AudioDevice : public QIODevice
{
public:
enum Channel {Mono, Left, Right, Both}; // these are mapped to combobox index so don't change
static char const * toString (Channel c)
{
return Mono == c ? "Mono" : Left == c ? "Left" : Right == c ? "Right" : "Both";
}
static Channel fromString (QString const& str)
{
QString s (str.toCaseFolded ().trimmed ().toLatin1 ());
return "both" == s ? Both : "right" == s ? Right : "left" == s ? Left : Mono;
}
bool open (OpenMode mode, Channel channel)
{
m_channel = channel;
// ensure we are unbuffered
return QIODevice::open (mode | QIODevice::Unbuffered);
}
bool isSequential () const {return true;}
size_t bytesPerFrame () const {return sizeof (qint16) * (Mono == m_channel ? 1 : 2);}
Channel channel () const {return m_channel;}
protected:
AudioDevice (QObject * parent = 0)
: QIODevice (parent)
{
}
void store (char const * source, size_t numFrames, qint16 * dest)
{
qint16 const * begin (reinterpret_cast<qint16 const *> (source));
for ( qint16 const * i = begin; i != begin + numFrames * (bytesPerFrame () / sizeof (qint16)); i += bytesPerFrame () / sizeof (qint16))
{
switch (m_channel)
{
case Mono:
*dest++ = *i;
break;
case Right:
*dest++ = *(i + 1);
break;
case Both: // should be able to happen but if it
// does we'll take left
Q_ASSERT (Both == m_channel);
case Left:
*dest++ = *i;
break;
}
}
}
qint16 * load (qint16 const sample, qint16 * dest)
{
switch (m_channel)
{
case Mono:
*dest++ = sample;
break;
case Left:
*dest++ = sample;
*dest++ = 0;
break;
case Right:
*dest++ = 0;
*dest++ = sample;
break;
case Both:
*dest++ = sample;
*dest++ = sample;
break;
}
return dest;
}
private:
Channel m_channel;
};
Q_DECLARE_METATYPE (AudioDevice::Channel);
#endif